Roll over stability control for an automotive vehicle

ABSTRACT

A stability control system ( 24 ) for an automotive vehicle as includes a plurality of sensors ( 28-37 ) sensing the dynamic conditions of the vehicle and a controller ( 26 ) that controls a distributed brake pressure to reduce a tire moment so the net moment of the vehicle is counter to the roll direction. The sensors include a speed sensor ( 30 ), a lateral acceleration sensor ( 32 ), a roll rate sensor ( 34 ), and a yaw rate sensor ( 20 ). The controller ( 26 ) is coupled to the speed sensor ( 30 ), the lateral acceleration sensor ( 32 ), the roll rate sensor ( 34 ), the yaw rate sensor ( 28 ). The controller ( 26 ) determines a roll angle estimate in response to lateral acceleration, roll rate, vehicle speed, and yaw rate. The controller ( 26 ) changes a tire force vector using brake pressure distribution in response to the relative roll angle estimate.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent application09/682,974 entitled “ROLL OVER STABILITY CONTROL FOR AN AUTOMOTIVEVEHICLE” filed on Nov. 5, 2001, now Pat. No. 6,529,803.

TECHNICAL FIELD

The present invention relates generally to a dynamic behavior controlapparatus for an automotive vehicle, and more specifically, to a methodand apparatus for controlling the roll characteristics of the vehicle bychanging a brake pressure distribution changing a steering angle orcombination of both.

BACKGROUND

Dynamic control systems for automotive vehicles have recently begun tobe offered on various products. Dynamic control systems typicallycontrol the yaw of the vehicle by controlling the braking effort at thevarious wheels of the vehicle. Yaw control systems typically compare thedesired direction of the vehicle based upon the steering wheel angle andthe direction of travel. By regulating the amount of braking at eachcorner of the vehicle, the desired direction of travel may bemaintained. Typically, the dynamic control systems do not address rollof the vehicle. For high profile vehicles in particular, it would bedesirable to control the roll over characteristic of the vehicle tomaintain the vehicle position with respect to the road. That is, it isdesirable to maintain contact of each of the four tires of the vehicleon the road.

Vehicle rollover and tilt control (or body roll) are distinguishabledynamic characteristics. Tilt control maintains the vehicle body on aplane or nearly on a plane parallel to the road surface. Roll overcontrol is maintaining the vehicle wheels on the road surface. Onesystem of tilt control is described in U.S. Pat. No. 5,869,943. The '943patent uses the combination of yaw control and tilt control to maintainthe vehicle body horizontal while turning. The system is used inconjunction with the front outside wheels only. To control tilt, a brakeforce is applied to the front out-side wheels of a turn. One problemwith the application of a brake force to only the front wheels is thatthe cornering ability of the vehicle may be reduced. Anotherdisadvantage of the system is that the yaw control system is used totrigger the tilt control system. During certain vehicle maneuvers, thevehicle may not be in a turning or yawing condition but may be in arollover condition. Such a system does not address preventing rolloverin a vehicle.

It would therefore be desirable to provide a roll stability system thatdetects a potential rollover condition as well as to provide a systemnot dependent upon a yaw condition.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a roll controlsystem for use in a vehicle that is not dependent upon the turningcondition of the vehicle.

In one aspect of the invention, stability control system for anautomotive vehicle includes a plurality of sensors sensing the dynamicconditions of the vehicle and a controller that controls a distributedbrake pressure to reduce a tire moment so the net moment of the vehicleis counter to the roll direction. The sensors include a speed sensor, alateral acceleration sensor, a roll rate sensor, and a yaw rate sensor.A controller is coupled to the speed sensor, the lateral accelerationsensor, the roll rate sensor, the yaw rate sensor. The controllerdetermines a roll angle estimate in response to lateral acceleration,roll rate, vehicle speed, and yaw rate. The controller determines abrake pressure distribution in response to the relative roll angleestimate. The controller may also use longitudinal acceleration andpitch rate to determine the roll angle estimate.

In a further aspect of the invention, a method of controlling rollstability of the vehicle comprises determining a roll angle estimate inresponse to lateral acceleration, roll rate, vehicle speed, and yawrate, and determining a brake pressure distribution in response to therelative roll angle estimate.

One advantage of the invention is that the turning radius of the vehicleis not affected by the roll stability control.

Other objects and features of the present invention will become apparentwhen viewed in light of the detailed description of the preferredembodiment when taken in conjunction with the attached drawings andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic rear view of a vehicle with force vectors nothaving a roll stability system according to the present invention.

FIG. 2 is a diagrammatic rear view of a vehicle with force vectorshaving a roll stability system according to the present invention.

FIG. 3 is a block diagram of a roll stability system according to thepresent invention.

FIG. 4 is a flow chart of a yaw rate determination according to thepresent invention.

FIG. 5 is a flow chart of roll rate determination according to thepresent invention.

FIG. 6 is a flow chart of a lateral acceleration determination accordingto the present invention.

FIG. 7 is a flow chart of chassis roll angle estimation andcompensation.

FIG. 8 is a flow chart of a relative roll calculation.

FIG. 9 is a flow chart of system feedback for the right side of thevehicle resulting in brake distribution force.

FIG. 10 is a flow chart of system feedback for the left side of thevehicle.

FIG. 11 is a flow chart of another embodiment similar to that of FIGS. 9and 10 resulting in change in steering position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an automotive vehicle 10 without a rolloverstability system of the present invention is illustrated with thevarious forces and moments thereon during a rollover condition. Vehicle10 has right and left tires 12 and 13 respectively. The vehicle may alsohave a number of different types of steering configurations includinghaving each of the front and rear wheels configured with anindependently controllable actuator, the front and rear wheels having aconventional type system in which both of the front wheels arecontrolled together and both of the rear wheels are controlled together,a system having conventional front steering and independentlycontrollable rear steering for each of the wheels or vice versa.Variation of a control system for each will be described below.Generally, the vehicle has a weight represented as M*g at the center ofgravity of the vehicle. A gravity moment 14 acts about the center ofgravity (CG) in a counter-clockwise direction. A tire moment 16 acts ina clockwise direction about the center of gravity. Thus, the net moment18 acting upon the vehicle is in a clockwise direction and thusincreases the roll angle 20 of the vehicle. The lateral force 22 at thetire 12 on the ground (tire vector) is a significant force to the leftof the diagram capable of overturning the vehicle if uncorrected.

Referring now to FIG. 2, a roll stability control system 24 is includedwithin vehicle 10, which is in a roll condition. The forces illustratedin FIG. 2 are given the same reference numerals as the forces andmoments in FIG. 1. In FIG. 2, however, roll stability controller 24reduces the tire moment 16 to provide a net moment 18 in acounter-clockwise direction. Thus, the tire vector or lateral force 22at tire 12 is reduced as well. This tendency allows the vehicle to tendtoward the horizontal and thus reduce angle 20.

Referring now to FIG. 3, roll stability control system 24 has acontroller 26 used for receiving information from a number of sensorswhich may include a yaw rate sensor 28, a speed sensor 30, a lateralacceleration sensor 32, a roll rate sensor 34, a steering angle sensor35, a longitudinal acceleration sensor 36, a pitch rate sensor 37 steerand a steering angle position sensor 39. Lateral acceleration, rollorientation and speed may be obtained using a global positioning system(Global Positioning System). Based upon inputs from the sensors,controller 26 controls a tire force vector by steering control 38 aswill be further described below or changing the steering angle of frontright actuator 40 a, front left actuator 40 b, rear left actuator 40 cand/or rear right actuator 40 d. As described above, two or more of theactuators may be simultaneously controlled. For example, in arack-and-pinion system, the two wheels coupled thereto aresimultaneously controlled. Brake control 42 controls the front rightbrake 44 a, the front left brake 44 b, the rear left brake 44 c, and theright rear brake 446 d. Based on the inputs from sensors 28 through 39,controller 26 determines a roll condition and controls the brakepressure of the brakes on the appropriate side of the vehicle and/orsteering angle. The braking pressure and/or steering angle is balancedon the side of the vehicle to be controlled between the front and rearbrakes to minimize the induced yaw torque and induced path deviation.Depending on the desired sensitivity of the system and various otherfactors, not all the sensors 28-39 may be used in a commercialembodiment.

Roll rate sensor 34 and pitch rate sensor 37 may sense the rollcondition of the vehicle based on sensing the height of one or morepoints on the vehicle relative to the road surface. Sensors that may beused to achieve this include a radar-based proximity sensor, alaser-based proximity sensor and a sonar-based proximity sensor.

Roll rate sensor 34 and pitch rate sensor 37 may also sense the rollcondition based on sensing the linear or rotational relativedisplacement or displacement velocity of one or more of the suspensionchasse components which may include a linear height or travel sensor, arotary height or travel sensor, a wheel speed sensor used to look for achange in velocity, a steering wheel position sensor, a steering wheelvelocity sensor and a driver heading command input from an electroniccomponent that may include steer by wire using a hand wheel or joystick.

The roll condition may also be sensed by sensing the force or torqueassociated with the loading condition of one or more suspension orchassis components including a pressure transducer in an act ofsuspension, a shock absorber sensor such as a load cell, a strain gauge,the steering system absolute or relative motor load, the steering systempressure of the hydraulic lines, a tire laterally force sensor orsensors, a longitudinal tire force sensor, a vertical tire force sensoror a tire sidewall torsion sensor.

The potential of a roll condition is associated with a zero normal loador a wheel lift condition on one or more of the wheels. A zero normalload, and thus a roll condition may be determined by sensing the forceor torque associated with the loading condition of one or moresuspension or chassis components including a pressure transducer in asuspension actuator. Similarly, a load cell or a strain gauge may bemounted to measure the force in a suspension component. The zero normalload condition may be used alone or in combination with otherdisplacement or inertial measurements to accurately monitor the vehicleroll condition.

The power steering system actuation can be monitored to infer the normalload on the steered wheels. The steering load can be monitored bymeasuring one or more of the absolute or relative motor load, thesteering system pressure of the hydraulic lines, tire lateral forcesensor or sensors, a longitudinal tire force sensor(s), vertical tireforce sensor(s) or tire sidewall torsion sensor(s) The steering systemmeasurements used depend on the steering system technology and thesensors available on the vehicle.

The roll condition of the vehicle may also be established by one or moreof the following translational or rotational positions, velocities oraccelerations of the vehicle including a roll gyro, the roll rate sensor34, the yaw rate sensor 28, the lateral acceleration sensor 32, avertical acceleration sensor, a vehicle longitudinal accelerationsensor, lateral or vertical speed sensor including a wheel-based speedsensor, a radar-based speed sensor, a sonar-based speed sensor, alaser-based speed sensor or an optical-based speed sensor.

Speed sensor 30 may be one of a variety of speed sensors known to thoseskilled in the art. For example, a suitable speed sensor may include asensor at every wheel that is averaged by controller 26. Preferably, thecontroller translates the wheel speeds into the speed of the vehicle.Yaw rate, steering angle, wheel speed and possibly a slip angle estimateat each wheel may be translated back to the speed of the vehicle at thecenter of gravity (V_CG). Various other algorithms are known to thoseskilled in the art. Speed may also be obtained from a transmissionsensor. For example, if speed is determined while speeding up or brakingaround a corner, the lowest or highest wheel speed may be not usedbecause of its error. Also, a transmission sensor may be used todetermine vehicle speed.

Referring now to FIG. 4, the yaw rate sensor 28 generates a raw yaw ratesignal (YR_Raw). A yaw rate compensated and filtered signal (YR_CompFlt)is determined. The velocity of the vehicle at center of gravity (V_CG),the yaw rate offset (YR_Offset) and the raw yaw rate signal from the yawrate sensor (YR_Raw) are used in a yaw rate offset initialization block45 to determine an initial yaw rate offset. Because this is an iterativeprocess, the yaw rate offset from the previous calculation is used byyaw rate offset initialization block 45. If the vehicle is not moving asduring startup, the yaw rate offset signal is that value which resultsin a compensated yaw rate of zero. This yaw rate offset signal helpsprovide an accurate reading. For example, if the vehicle is at rest, theyaw rate signal should be zero. However, if the vehicle is reading a yawrate value then that yaw rate value is used as the yaw rate offset. Theyaw rate offset signal along with the raw yaw rate signal is used in theanti-windup logic block 46. The anti-windup logic block 46 is used tocancel drift in the yaw rate signal. The yaw rate signal may have driftover time due to temperature or other environmental factors. Theanti-windup logic block also helps compensate for when the vehicle istraveling constantly in a turn for a relatively long period. Theanti-windup logic block 46 generates either a positive compensation OKsignal (Pos Comp OK) or a negative compensation OK signal (Neg Comp OK).Positive and negative in this manner have been arbitrarily chosen to bethe right and left direction with respect to the forward direction ofthe vehicle, respectively. The positive compensation OK signal, thenegative compensation OK signal and the yaw rate offset signal areinputs to yaw rate offset compensation logic block 47.

The yaw rate offset compensation logic block 47 is used to take dataover a long period of time. The data over time should have an averageyaw of zero. This calculation may be done over a number of minutes. Ayaw rate offset signal is generated by yaw rate offset compensationlogic 47. A summing block 48 sums the raw yaw rate signal and the yawrate offset signal to obtain a yaw rate compensated signal (YR_Comp).

A low pass filter 49 is used to filter the yaw rate compensated signalfor noise. A suitable cutoff frequency for low pass filter 49 is 20 Hz.

Referring now to FIG. 5, a roll rate compensated and filtered signal(RR_CompFlt). The roll rate compensated and filtered signal is generatedin a similar manner to that described above with respect to yaw rate. Aroll rate offset initialization block 50 receives the velocity at centerof gravity signal and a roll rate offset signal. The roll rate offsetsignal is generated from a previous iteration. Like the yaw rate, whenthe vehicle is at rest such as during startup, the roll rate offsetsignal is zero.

A roll rate offset compensation logic block 52 receives the initializedroll rate offset signal. The roll rate offset compensation logicgenerates a roll rate offset signal which is combined with the roll rateraw signal obtained from the roll rate sensor in a summing block 54. Aroll rate compensated signal (RR_Comp) is generated. The roll ratecompensated signal is filtered in low pass filter 56 to obtain the rollrate compensated and filtered signal that will be used in latercalculations.

Referring now to FIG. 6, the raw lateral acceleration signal (Lat AccRaw) is obtained from lateral acceleration sensor 32. The raw lateralacceleration signal is filtered by a low pass filter to obtain thefiltered lateral acceleration signal (Lat Acc Flt). The filter, forexample, may be a 20 Hz low pass filter.

Referring now to FIG. 7, a roll angle estimation signal (RollAngleEst)is determined by chassis roll estimation and compensation procedure 62.Block 64 is used to obtain a longitudinal vehicle speed estimation atthe center of gravity of the vehicle. Various signals are used todetermine the longitudinal vehicle speed at the center of gravityincluding the velocity of the vehicle at center of gravity determined ina previous loop, the compensated and filtered yaw rate signal determinedin FIG. 4, the steering angle, the body slip angle, the front left wheelspeed, the front right wheel speed, the rear left wheel speed, and therear right wheel speed.

The new velocity of the center of gravity of the vehicle is an input tobody roll angle initialization block 66. Other inputs to body roll angleinitialization block 66 include roll angle estimate from the previousloop and a filtered lateral acceleration signal derived in FIG. 6. Anupdated roll angle estimate is obtained from body roll angleinitialization. The updated roll angle estimate, the compensation andfiltered roll rate determination from FIG. 5, and the time of the loopis used in body roll angle integration block 68. The updated roll angleestimate is equal to the loop time multiplied by the compensated andfiltered roll rate which is added to the previous roll angle estimateobtained in block 66. The updated roll angle estimate is an input toroll angle estimate offset compensation block 70.

The velocity at the center of gravity of the vehicle is also an input toinstantaneous roll angle reference block 72. Other inputs toinstantaneous roll angle reference block 72 include the compensated andfiltered yaw rate from FIG. 4 and the filtered lateral accelerationsignal from FIG. 6. The following formula is used to determine areference roll angle:

ReferenceRollAngle=ARC Sin [1/g(VCG*YRCompFlt−LatAccFlt)]

Where g is the gravitational constant 9.81 m/s².

The reference roll angle from block 72 is also an input to roll angleestimate offset compensation. The updated roll angle estimation is givenby the formula: $\begin{matrix}{{RollAngleEst} = {{{RollAngleEst}\quad ( {{from}\quad {Block}\quad 68} )} +}} \\{( {{{Reference}\quad {Roll}\quad {Angle}} - {{RollAngleEst}\quad ( {{Block}\quad 68} )}} )\frac{{loop}\quad {time}}{Tau}}\end{matrix}$

Where Tau is a time constant and may be a function of steering velocity,LatAcc and V-CG. A suitable time constant may, for example, be 30seconds.

Referring now to FIG. 8, a relative roll angle estimation(RelativeRollAngleEst) and a road bank angle estimate signal isdetermined. The first step of the relative roll angle calculationinvolves the determination of road bank angle compensation time constant(Tau) block 72. The velocity at the center of gravity, the steeringvelocity and the filtered lateral acceleration signal from FIG. 6 areused as inputs. A compensated and filtered roll rate (RR_CompFlt) isused as an input to a differentiator 74 to determine the rollacceleration (Roll Acc). Differentiator 74 takes the difference betweenthe compensated and filtered roll rate signal from the previous loop andthe compensated and filtered roll rate from the current loop divided bythe loop time to attain the roll acceleration. The roll accelerationsignal is coupled to a low pass filter 76. The filtered rollacceleration signal (Roll Acc Flt), roll angle estimate, the filteredlateral acceleration signal and the loop time are coupled to chassisrelative roll observer block 78. The chassis roll observer 78 determinesthe model roll angle estimation (Model Roll Angle Est). The model rollangle is a stable estimation of the roll dynamics of the vehicle whichallows the estimates to converge to a stable condition over time.

From the model roll angle estimation from block 78, the initial relativeroll angle estimation from block 72, a road bank angle initializationfrom a block 79 loop time and a roll angle estimate, road bank anglecompensation block 80 determines a new road bank angle estimate. Theformula for road bank angle is:${RoadBankAngleEst} = {\frac{LoopTime}{TauRoad\_ Bank}*( {{RollAngleEst} - \begin{pmatrix}{{ModelRollAngle} +} \\{RoadBankAngleEst}\end{pmatrix}} )}$

The roll angle estimate may be summed with the road bank angle estimatefrom block 80 in summer 82 to obtain a relative roll angle estimate. Theroad bank angle estimate may be used by other dynamic control systems.

Referring now to FIG. 9, the relative roll angle estimate from FIG. 8and a relative roll deadband are summed in summer 84 to obtain an upperroll error. The upper roll error is amplified in KP_Roll Amplifier 86and is coupled to summer 88. The roll rate compensated and filteredsignal from FIG. 5 is coupled to KD_Roll Amplifier 90. The amplifiedroll rate signal is coupled to summer 88. The filtered roll accelerationsignal from block 8 is coupled to KDD_Roll Amplifier 82. The amplifiedsignal is also coupled to summer 88. The proportioned sum of theamplified signals is the right side braking force effort. From this, theright side brake force distribution calculation block 94 is used todetermine the distribution of brake pressure between the front and rearwheels. The front right normal load estimate and the rear right normalload estimate are inputs to block 94. The front right roll controldesired pressure and the right rear roll control desire pressure areoutputs of block 94. The block 94 proportions the pressure between thefront right and rear right signals to prevent roll. The front right, forexample, is proportional according to the following formula:${{FR}\quad {desired}\quad {pressure}} = {{Right}\quad {side}\quad {braking}\quad {effort}\quad ( \frac{FRNormal}{{FR} + {RR}} )}$

The output of block 94 is used by the brake controller of FIG. 3 toapply brake pressure to the front right and rear right wheels. The brakecontroller factors in inputs such as the brake pressure currentlyapplied to the vehicle through the application of pressure by the driveron the brake pedal. Other inputs include inputs from other dynamiccontrol systems such as a yaw control system.

Referring now to FIG. 10, a similar calculation to that of FIG. 9 isperformed for the left side of the vehicle. The relative roll angleestimate and relative roll deadband are inputs to summing block 96.However, the signs are changed to reflect that the left side of thevehicle is a negative side of the vehicle. Therefore, relative rollangle estimate and relative roll deadband are purely summed together 96in summing block 96 to obtain the lower roll error. The lower roll erroris passed through KP_Roll amplifier 98. The compensated and filteredroll rate is passed through KD_Roll amplifier 100 and the filtered rollacceleration signal is passed through KDD_Roll amplifier 102. Theinverse of the signals from amplifiers 98, 100 and 102 are input andsummed in summer 104 to obtain the left side braking effort.

A left side brake force distribution calculation block 106 receives theleft side braking effort from summer 104. The front left normal loadestimate and the rear left normal load estimate. In a similar manner tothat above, the front left and rear left roll control brake pressuresare determined. By properly applying the brakes to the vehicle, the tiremoment is reduced and the net moment of the vehicle is counter to a rolldirection to reduce the roll angle and maintain the vehicle in ahorizontal plane.

Referring now to FIG. 11, a change in steering angle may be effectuatedrather than or in combination with a change in brake force distribution.In either case, however, the tire force vector is changed. In FIG. 11,the same reference numerals as those in FIGS. 9 and 10 are used but areprimed. Everything prior to blocks 88′ and 104′ is identical. Blocks 88′and 104′ determine right side steering effort and left side steeringeffort, respectively.

The proportioned sum of the amplified signals is the right side steeringtire correction. The rear (and front) steering actuator control signalsare calculated from the tire corrections, the front and rear steerangles or the actuator positions, the vehicle side slip angle, thevehicle yaw rate and vehicle speed. Increased accuracy and robustnesscan be achieved by including tire normal load estimates and/or tire slipratios. In the steering angle and effort correction block 94, the tireslip angles are calculated and used to determine the corrections to therear (and front) steer angles that will reduce the tire lateral forcesand reduce the vehicle roll angle. Block 94 also calculates the actuatorcontrol signals necessary to achieve the desired tire steeringcorrections.

The measured steering actuator positions are inputs to block 94. Thechange in the actuator direction and effort amounts and duration areoutputs of block 94. The block 94 determines the appropriate directionand force amount to apply to the steering actuators to prevent roll.

The output of block 94 is used by the steering controller 38 of FIG. 3to apply the desired steering to the front and/or rear wheels dependingon the type of steering system. The steering controller factors ininputs such as the current steering position and the dynamics of thevehicle. Other inputs may include inputs from other dynamic controlsystems such as a yaw control system. In a production ready embodiment,the vehicle design characteristics will be factored into the desiredcontrol based on the sensor outputs.

The bottom portion of FIG. 9 is similar to the top, however, the signsare changed to reflect that the left side of the vehicle is a negativeside of the vehicle. Therefore, relative roll angle estimate andrelative roll deadband are purely summed together 96 in summing block 96to obtain the lower roll error. The lower roll error is passed throughKP_Roll amplifier 98. The compensated and filtered roll rate is passedthrough KD_Roll amplifier 100 and the filtered roll acceleration signalis passed through KDD_Roll amplifier 102. The inverse of the signalsfrom amplifiers 98, 100 and 102 are input and summed in summer 104 toobtain the desired left actuator control.

By properly applying a desired steering control to the vehicle, the tiremoment is reduced and the net moment of the vehicle is counter to a rolldirection to reduce the roll angle and maintain the vehicle in ahorizontal plane.

If both steering and brake distribution are used controller 26 will beused to apportion the amount of correction provided by steering andbrake distribution. The amount of apportionment will depend on the rollrate and other variables for the particular vehicle. The amount ofapportionment will thus be determined for each vehicle. For example,higher profile vehicles will be apportioned differently from a lowprofile vehicle.

In operation, various types of steering control may be performeddepending on the vehicle characteristics and the steering system. Forexample, as described above a rack system may be controlled to provide adesired change in the rear steering angle temporarily to preventrollover while leaving the front wheels unchanged. Of course, thedirection of the front wheels could also be change when the reardirection is changed.

In a system having independently actuable front wheels, the relativesteering angle between the front wheels may be changed in response todetected roll by steering control 38 without changing the position orcontrolling the position of the rear wheel. This may be done byindependent control of the front wheels or simultaneous control of thefront wheels.

In a system having independently actuable rear wheels, the relativesteering angle between the front wheels may be changed in response todetected roll by steering control 38 without changing the position orcontrolling the position of the front wheels. This may be done byindependent control of the rear wheels or simultaneous control of therear wheels.

As described above the longitudinal acceleration sensor and a pitch ratesensor may be incorporated into the above tire force vectordetermination. These sensors may be used as a verification as well as anintegral part of the calculations. For example, the pitch rate or thelongitudinal acceleration or both can be used to construct a vehiclepitch angle estimate. This estimate along with its derivative can beused to improve the calculation of the vehicle roll angle. An example ofhow the rate of change of the vehicle roll angle using theses variablesmay be constructed is: $\begin{matrix}\begin{matrix}{{GlobalRR} \approx {{RRComp\_ Flt} + {PitchRateCompFlt}}} \\{( {{- {YawRate}} + {{Sin}\quad ({GlobalRollAngleEst})*{Tan}\quad ({VehiclePitchAngleEst})}} ) +}\end{matrix} \\( {{YawRateCompFlt}*{Cos}\quad ({GlobalRR})*{Tan}\quad ({PitchAngleEst})} )\end{matrix}$

Where PitchRateCompFlt is a compensated and filtered pitch rate signal,GlobalRollAngleEst is an estimated global roll angle,VehiclePitchAngleEst is an estimated vehicle pitch angle estimate, andGlobalRR is a global roll rate signal. Of course, those skilled in theart may vary the above based upon various other factors depending on theparticular system needs.

While particular embodiments of the invention have been shown anddescribed, numerous variations and alternate embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

What is claimed is:
 1. A method of controlling roll stability of avehicle comprising the steps of: determining a roll angle of thevehicle; and generating a tire moment in response to the roll angle sothat a net moment on the vehicle is counter to a roll direction.
 2. Amethod as recited in claim 1 wherein the tire moment approaches agravity moment.
 3. A method as recited in claim 1 wherein determining aroll angle comprises determining a roll angle in response to a lateralacceleration.
 4. A method as recited in claim 1 wherein determining aroll angle comprises determining a roll angle in response to a lateralacceleration and yaw rate.
 5. A method as recited in claim 1 whereindetermining a roll angle comprises determining a roll angle in responseto a lateral acceleration, vehicle speed and yaw rate.
 6. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a lateral acceleration and a steering velocity.
 7. A methodas recited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a roll rate.
 8. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a vehicle speed.
 9. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a yaw rate a pitch angle.
 10. Amethod as recited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a pitch rate.
 11. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a pitch angle.
 12. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a global positioning systemsignal.
 13. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a steeringangle.
 14. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a steeringvelocity.
 15. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a wheel speed.16. A method as recited in claim 1 wherein determining a roll anglecomprises determining a roll angle in response to a wheel normal loadestimate.
 17. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a road bankangle.
 18. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a rollacceleration.
 19. A method as recited in claim 1 wherein determining aroll angle comprises determining a roll angle in response to alongitudinal acceleration.
 20. A method as recited in claim 1 whereindetermining a roll angle comprises determining a roll angle in responseto a reference roll angle.
 21. A method as recited in claim 1 whereindetermining a roll angle comprises determining a roll angle in responseto a relative roll angle.
 22. A method as recited in claim 1 whereindetermining a roll angle comprises determining a roll angle in responseto a road bank angle and a previous roll angle estimate.
 23. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to a road bank angle and areference roll angle.
 24. A method as recited in claim 1 whereindetermining a roll angle comprises determining a roll angle in responseto a body roll angle initialization.
 25. A method as recited in claim 24wherein the body roll angle initialization is determined in response toa roll angle estimate and a lateral acceleration.
 26. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to an instantaneous roll anglereference.
 27. A method as recited in claim 26 wherein the instantaneousroll angle reference is determined in response to a vehicle speed, a yawrate and a lateral acceleration.
 28. A method as recited in claim 1wherein the roll angle estimate is determined in response to a referenceroll angle and a body roll integration.
 29. A method as recited in claim1 wherein determining a roll angle comprises determining a roll angle inresponse to a roll angle estimate.
 30. A method as recited in claim 29wherein the roll angle estimate is determined in response to a referenceroll angle and a body roll integration.
 31. A method as recited in claim1 wherein determining a roll angle comprises determining a roll angle inresponse to a model roll angle.
 32. A method as recited in claim 31wherein the model roll angle is determined in response to a chassis rollobserver.
 33. A method as recited in claim 1 wherein determining a rollangle comprises determining a roll angle in response to a road bankangle time constant.
 34. A method as recited in claim 33 wherein theroad bank angle time constant is determined in response to a steeringvelocity, a lateral acceleration and a vehicle speed.
 35. A method asrecited in claim 1 wherein determining a roll angle comprisesdetermining a roll angle in response to body slip.
 36. A method ofcontrolling roll stability of a vehicle comprising the steps of:determining a roll angle estimate; and generating a tire moment inresponse to a roll angle estimate, so that a net moment on the vehicleis counter to a roll direction.
 37. A method as recited in claim 36wherein the tire moment approaches a gravity moment.
 38. A method asrecited in claim 36 determining a roll angle estimate comprisesdetermining a roll angle estimate in response to a lateral acceleration.39. A method as recited in claim 36 determining a roll angle estimatecomprises determining a roll angle estimate in response to a lateralacceleration and yaw rate.
 40. A method as recited in claim 36determining a roll angle estimate comprises determining a roll angleestimate in response to a lateral acceleration, vehicle speed and yawrate.
 41. A method as recited in claim 36 wherein determining a rollangle estimate comprises determining a lateral acceleration and asteering velocity.
 42. A method as recited in claim 36 determining aroll angle estimate comprises determining a roll angle estimate inresponse to a roll rate.
 43. A method as recited in claim 36 determininga roll angle estimate comprises determining a roll angle estimate inresponse to a vehicle speed.
 44. A method as recited in claim 36determining a roll angle estimate comprises determining a roll angleestimate in response to a yaw rate a pitch angle.
 45. A method asrecited in claim 36 determining a roll angle estimate comprisesdetermining a roll angle estimate in response to a pitch rate.
 46. Amethod as recited in claim 36 determining a roll angle estimatecomprises determining a roll angle estimate in response to a pitchangle.
 47. A method as recited in claim 36 determining a roll angleestimate comprises determining a roll angle estimate in response to aglobal positioning system signal.
 48. A method as recited in claim 36determining a roll angle estimate comprises determining a roll angleestimate in response to a steering angle.
 49. A method as recited inclaim 36 determining a roll angle estimate comprises determining a rollangle estimate in response to a steering velocity.
 50. A method asrecited in claim 36 determining a roll angle estimate comprisesdetermining a roll angle estimate in response to a wheel speed.
 51. Amethod as recited in claim 36 determining a roll angle estimatecomprises determining a roll angle estimate in response to a wheelnormal load estimate.
 52. A method as recited in claim 36 determining aroll angle estimate comprises determining a roll angle estimate inresponse to a road bank angle.
 53. A method as recited in claim 36determining a roll angle estimate comprises determining a roll angleestimate in response to a roll acceleration.
 54. A method as recited inclaim 36 determining a roll angle estimate comprises determining a rollangle estimate in response to a longitudinal acceleration.
 55. A methodas recited in claim 36 wherein determining a roll angle estimatecomprises determining a roll angle estimate in response to a referenceroll angle.
 56. A method as recited in claim 36 wherein determining aroll angle estimate comprises determining a roll angle estimate inresponse to a relative roll angle.
 57. A method as recited in claim 36wherein determining a roll angle estimate comprises determining a rollangle estimate in response to a road bank angle and a previous rollangle estimate.
 58. A method as recited in claim 36 wherein determininga roll angle estimate comprises determining a roll angle estimate inresponse to a road bank angle and a reference roll angle.
 59. A methodas recited in claim 36 wherein determining a roll angle estimatecomprises determining a roll angle estimate in response to a body rollangle initialization.
 60. A method as recited in claim 59 wherein thebody roll angle initialization is determined in response to a lateralacceleration.
 61. A method as recited in claim 36 wherein determining aroll angle estimate comprises determining a roll angle estimate inresponse to an instantaneous roll angle reference.
 62. A method asrecited in claim 61 wherein the instantaneous roll angle reference isdetermined in response to a vehicle speed, a yaw rate and a lateralacceleration.
 63. A method as recited in claim 36 wherein the roll angleestimate is determined in response to a reference roll angle and a bodyroll integration.
 64. A method as recited in claim 36 whereindetermining a roll angle comprises determining a roll angle in responseto a model roll angle.
 65. A method as recited in claim 64 wherein themodel roll angle is determined in response to a chassis roll observer.66. A method as recited in claim 36 wherein determining a roll angleestimate comprises determining a roll angle estimate in response to aroad bank angle time constant.
 67. A method as recited in claim 66wherein the road bank angle time constant is determined in response to asteering velocity, a lateral acceleration and a vehicle speed.
 68. Amethod as recited in claim 36 wherein determining a roll angle estimatecomprises determining a roll angle estimate in response to body slip.69. A method of controlling roll stability of a vehicle comprising thesteps of: determining a roll responsive control signal; and generating atire moment in response to the roll responsive control signal so that anet moment on the vehicle is counter to a roll direction.
 70. A methodas recited in claim 69 wherein the tire moment approaches a gravitymoment.
 71. A method as recited in claim 69 wherein determining a rollresponsive signal comprises determining a roll responsive control signalin response to a lateral acceleration.
 72. A method as recited in claim69 wherein determining a roll responsive control signal comprisesdetermining a roll responsive control signal in response to a lateralacceleration and yaw rate.
 73. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining aroll responsive control signal in response to a lateral acceleration,vehicle speed and yaw rate.
 74. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining alateral acceleration and a steering velocity.
 75. A method as recited inclaim 69 wherein determining a roll responsive control signal comprisesdetermining a roll responsive control signal in response to a roll rate.76. A method as recited in claim 69 wherein determining a rollresponsive control signal comprises determining a roll responsivecontrol signal in response to a vehicle speed.
 77. A method as recitedin claim 69 wherein determining a roll responsive control signalcomprises determining a roll responsive control signal in response to ayaw rate a pitch angle.
 78. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining aroll responsive control signal in response to a pitch rate.
 79. A methodas recited in claim 69 wherein determining a roll responsive controlsignal comprises determining a roll responsive control signal inresponse to a pitch angle.
 80. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining aroll responsive control signal in response to a global positioningsystem signal.
 81. A method as recited in claim 69 wherein determining aroll responsive control signal comprises determining a roll responsivecontrol signal in response to a steering angle.
 82. A method as recitedin claim 69 wherein determining a roll responsive control signalcomprises determining a roll responsive control signal in response to asteering velocity.
 83. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining aroll responsive control signal in response to a wheel speed.
 84. Amethod as recited in claim 69 wherein determining a roll responsivecontrol signal comprises determining a roll responsive control signal inresponse to a wheel normal load estimate.
 85. A method as recited inclaim 69 wherein determining a roll responsive control signal comprisesdetermining a roll responsive control signal in response to a road bankangle.
 86. A method as recited in claim 69 wherein determining a rollresponsive control signal comprises determining a roll responsivecontrol signal in response to a roll acceleration.
 87. A method asrecited in claim 69 wherein determining a roll responsive control signalcomprises determining a roll responsive control signal in response to alongitudinal acceleration.
 88. A method as recited in claim 69 whereindetermining a roll responsive control signal comprises determining aroll responsive control signal in response to a roll angle.
 89. A methodas recited in claim 69 wherein determining a roll responsive controlsignal comprises determining a roll responsive control signal inresponse to a reference roll angle.
 90. A method as recited in claim 69wherein determining a roll responsive control signal comprisesdetermining a roll responsive control signal in response to a relativeroll angle.
 91. A method as recited in claim 69 wherein determining aroll responsive control signal comprises determining a roll responsivecontrol signal in response to a road bank angle and a previous rollangle estimate.
 92. A method as recited in claim 69 wherein determininga roll responsive control signal comprises determining a roll responsivecontrol signal in response to a road bank angle and a reference rollangle.
 93. A method as recited in claim 69 wherein determining a rollresponsive control signal comprises determining a roll responsivecontrol signal in response to a body roll angle initialization.
 94. Amethod as recited in claim 93 wherein the body roll angle initializationis determined in response to a roll angle estimate and a lateralacceleration.
 95. A method as recited in claim 69 wherein determining aroll responsive control signal comprises determining a roll responsivecontrol signal in response to an instantaneous roll angle reference. 96.A method as recited in claim 69 wherein the roll angle signal referenceis determined in response to a vehicle speed, a yaw rate and a lateralacceleration.
 97. A method as recited in claim 69 wherein determining aroll responsive control signal comprises determining a roll responsivecontrol signal in response to a roll angle estimate.
 98. A method asrecited in claim 69 wherein the roll responsive control signal isdetermined in response to a reference roll angle and a body rollintegration.
 99. A method as recited in claim 69 wherein determining aroll responsive control signal comprises determining a roll responsivecontrol signal in response to a model roll angle.
 100. A method asrecited in claim 99 wherein the model roll responsive control signal isdetermined in response to a chassis roll observer.
 101. A method asrecited in claim 69 wherein determining a roll responsive control signalcomprises determining a roll responsive control signal in response to aroad bank angle time constant.
 102. A method as recited in claim 101wherein the road bank angle time constant is determined in response to asteering velocity, a lateral acceleration and a vehicle speed.
 103. Amethod as recited in claim 69 wherein determining a roll responsivecontrol signal comprises determining a roll responsive control signal inresponse to body slip.
 104. A method of controlling roll stability of avehicle comprising the steps of: determining a vehicle roll condition;and generating a tire moment in response to the vehicle roll conditionso that a net moment on the vehicle is counter to a roll direction. 105.A method as recited in claim 104 wherein the tire moment approaches agravity moment.
 106. A method as recited in claim 104 whereindetermining a vehicle roll condition comprises determining a vehicleroll condition in response to a lateral acceleration.
 107. A method asrecited in claim 104 wherein determining a vehicle roll conditioncomprises determining a vehicle roll condition in response to a lateralacceleration and a yaw rate.
 108. A method as recited in claim 104wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a lateral acceleration, a yaw rateand a vehicle speed.
 109. A method as recited in claim 104 whereindetermining a vehicle roll condition comprises determining a lateralacceleration and a steering velocity.
 110. A method as recited in claim104 wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a roll rate.
 111. A method asrecited in claim 104 wherein determining a vehicle roll conditioncomprises determining a vehicle roll condition in response to a vehiclespeed.
 112. A method as recited in claim 104 wherein determining avehicle roll condition comprises determining a vehicle roll condition inresponse to a yaw rate a pitch angle.
 113. A method as recited in claim104 wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a pitch rate.
 114. A method asrecited in claim 104 wherein determining a vehicle roll conditioncomprises determining a vehicle roll condition in response to a pitchangle.
 115. A method as recited in claim 104 wherein determining avehicle roll condition comprises determining a vehicle roll condition inresponse to a global positioning system signal.
 116. A method as recitedin claim 104 wherein determining a vehicle roll condition comprisesdetermining a vehicle roll condition in response to a steering angle.117. A method as recited in claim 104 wherein determining a vehicle rollcondition comprises determining a vehicle roll condition in response toa steering velocity.
 118. A method as recited in claim 104 whereindetermining a vehicle roll condition comprises determining a vehicleroll condition in response to a wheel speed.
 119. A method as recited inclaim 104 wherein determining a vehicle roll condition comprisesdetermining a vehicle roll condition in response to a wheel normal loadestimate.
 120. A method as recited in claim 104 wherein determining avehicle roll condition comprises determining a vehicle roll condition inresponse to a road bank angle.
 121. A method as recited in claim 104wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a roll acceleration.
 122. A methodas recited in claim 104 wherein determining a vehicle roll conditioncomprises determining a vehicle roll condition in response to alongitudinal acceleration.
 123. A method as recited in claim 104 whereindetermining a vehicle roll condition comprises determining a vehicleroll condition in response to a roll angle.
 124. A method as recited inclaim 104 wherein determining a vehicle roll condition comprisesdetermining a vehicle roll condition in response to a reference rollangle.
 125. A method as recited in claim 104 wherein determining avehicle roll condition comprises determining a vehicle roll condition inresponse to a relative roll angle.
 126. A method as recited in claim 104wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a road bank angle and a previousroll angle estimate.
 127. A method as recited in claim 104 whereindetermining a vehicle roll condition comprises determining a vehicleroll condition in response to a road bank angle and a reference rollangle.
 128. A method as recited in claim 104 wherein determining avehicle roll condition comprises determining a vehicle roll condition inresponse to a body roll angle initialization.
 129. A method as recitedin claim 128 wherein the body roll angle initialization is determined inresponse to a roll angle estimate and a lateral acceleration.
 130. Amethod as recited in claim 104 wherein determining a vehicle rollcondition comprises determining a vehicle roll condition in response toan instantaneous roll angle reference.
 131. A method as recited in claim130 wherein the instantaneous roll angle reference is determined inresponse to a vehicle speed, a yaw rate and a lateral acceleration. 132.A method as recited in claim 104 wherein determining a vehicle rollcondition comprises determining a vehicle roll condition in response toa roll angle estimate.
 133. A method as recited in claim 132 wherein theroll angle estimate is determined in response to a reference roll angleand a body roll integration.
 134. A method as recited in claim 104wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a model roll angle.
 135. A methodas recited in claim 134 wherein the model roll angle is determined inresponse to a chassis roll observer.
 136. A method as recited in claim104 wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to a road bank angle time constant.137. A method as recited in claim 136 wherein the road bank angle timeconstant is determined in response to a steering velocity, a lateralacceleration and a vehicle speed.
 138. A method as recited in claim 104wherein determining a vehicle roll condition comprises determining avehicle roll condition in response to body slip.